This invention relates to a brittle body which is prepared to be destroyed later and relates also to a method of destroying the same. More particularly, this invention relates to a dental working cast which can be destroyed to take out a denture therefrom without damaging the denture and relates also to a method of destroying the same.
Denture is generally classified into a full denture and a partial denture. According to a prior art method of producing such dentures, an impression is first taken from the oral cavity of a patient, and slurry of gypsum is then poured into this impression to obtain a dental working cast. Then, a wax bite rim is formed on the working cast, and artificial teeth are arranged on the wax bite rim. The working cast having the artificial teeth arranged thereon is then placed in a flask, and, while pouring slurry of gypsum into the flask to embed the working cast in the block of gypsum, they are heated to fuse away the wax thereby obtaining a negative. A resin is then charged into the negative. Subsequently, the negative having the resin charged therein is heated to cure the resin, and the working cast containing the denture formed by the combination of the resin and the artificial teeth embedded in the working cast is deflasked. Thereafter, the denture is dug out of the working cast to separate it from the working cast. The gypsum used to form the working cast is ordinary gypsum, hard gypsum, super-hard gypsum or the like. For separating the denture from the working cast, a tool such as a plaster forceps is employed to destroy the working cast. Therefore, considerable skill is required, and, also, much labor and a large length of time are required for the removing of the denture. It is the fact that several dentures at the most can be separated in a day. Also, such a method has frequently given rise to breakdown or permanent deformation of a denture.
With a view to solve the above problem, the applicant has proposed a method of destroying such a brittle mold by the use of an expandable splitting agent capable of expanding by hydration, as filed in Japanese OPI Nos. 60-185546 and 60/193456 (1985). Application of this method to the working cast described above has successfully solved the prior art problem pointed out above.
However, in the method proposed already by the applicant, it is necessary to bore a hole in the working cast by a drilling machine such as a small-sized electric drill for charging the expansive splitting agent capable of expanding by hydration into the working cast. Therefore, the drilling operation must be carefully done so as not to impair or damage the artificial teeth embedded in the working cast, and, in addition, the method involves a problem of emvironmental pollution by shavings produced as a result of drilling. Also, there is a limit in the repeated use of the electric drill, and the durability of the electric drill has posed another problem.